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Lab Microtunnel Measures Emissions More Accurately

University of Minnesota researchers have built a laboratory microtunnel they say will provide a more accurate picture of hog manure emission reduction technologies

Dec 15, 2007

University of Minnesota researchers have built a laboratory microtunnel they say will provide a more accurate picture of hog manure emission reduction technologies.

The lab-based model eliminates season, climate and site variants, and leaves only a true comparison between control and treatment efforts aimed at reducing gas and odor emissions.

Determining gas and odor emissions in a controlled environment will also decrease the cost per sample to about 25% of field samples.

Measuring gas and odor emissions in the field is a challenging process with time and space factors influencing emission rates. Detailed on-farm emission measurements are not easily transferable to other sites with different genetics, feeding programs, manure management systems, geographic areas, etc.

This study focused on developing and testing a laboratory method to study the relationship of manure parameters and environmental conditions to manure emission rates.

A team of investigators developed a lab-scale method using a small aluminum wind tunnel to measure ammonia (NH3), hydrogen sulfide (H2S) and odor. This method was tested using 83 manure samples from 20 livestock farms throughout Minnesota. Findings are summarized in Table 1.

The microtunnel focused on airflow rates representing 0.5 to 2.0 mph wind speeds. The microtunnel was able to consistently detect differences in gas and odor emissions from different manure types, manure sources, manure solid contents and airflow rates. Ammonia emission rates agreed with field emission rates reported. Hydrogen sulfide and odor emission rates were somewhat higher than previous field research.

Those early results show promise for this new laboratory technique in testing gas and odor concentrations found in hog manure, determining emission rates and differentiating manure sources and manure types.

In other work, researchers studied the impact of manure agitation with the microtunnel. Slow stirring without surface disruption reduced ammonia emissions by 30% and increased hydrogen sulfide emissions by 2800%. Eight minutes after stirring slurry stopped, emission rates returned to previous levels.

When diluted manure was measured for emissions, each dilution level lowered gas emissions in a linear pattern. But the odor pattern was more of a bell-shaped curve, meaning that as manure became diluted, some samples attained greater odor strength.

To study the impact of sample storage time on emissions in the microtunnel, manure was stored up to nine days at cold temperatures (40°F) and/or room temperature (72-76°F). Overall, the ammonia emission rate increased about 8%/day when stored at the warm temperature, possibly due to increased microorganism activity. Hydrogen sulfide emissions decreased about 6%/day.

Development and testing of the microtunnel was funded by the National Research Initiative Air Quality Program, Cooperative States Research, Education and Extension Service, USDA.

In future collaboration with Iowa State University, accuracy and repeatability of the microtunnel is being tested for emissions of volatile organic chemicals. The microtunnel is also being modified and tested for its value in determining emission rates from a solid surface (dry manure and soil after manure application).